Cathode bay tube



May 16, 1939. P. T. FARNswoRTH CATHODE RAY TUBE Filed June l, 1956 INI/ENTORT PH/LO 7T FA RNSWORTH.

l El .2.

V i i ATTORNEYS.

Patented May 16, 1939 UNITED sTA'rlEs cA'rnona my 'rUmt Philo T. Farnsworth, San Francisco, Calif., as-

signor, by mesne assignments, to- Farnsworth Television Radio Corporation, Dover, Del., a corporation o! Delaware Animation June 1, 193s, serial No. 82,887

' z claim. '(ol. .25o-161) My invention relates to oscillcgraphic tu and more particularly to an oscillographic tube wherein a luminous spot of small size may be produced.

V Among-the objects of my invention are: to providean oscillograph capable of producing a luminous spot of small size to provide. a means forv vmaintaining electrons .in an oscillographic tube in parallel array between -cathodeand screen; to

l0 providel a. means in an oscillographicv tube for preventing dispersione!! electrons betweencathfv ode and screen to provides. concentrating means vacting on the electron beam in an oscillographic tube; to provide a means in an oscillographicl tube for applying a magnetic field directed to 1 maintain electrons in parallel relationship betweencathode and screen; "to provide a simple and eiiicient oscillographic tube having high. defi- 21g-coil inacathoderaytube.

' Other objects 'of my invention willb'e apparent or willfbe' specifically p'ointedrcutin the descripnition, and toprovide an internalconcentrating vtion forming. a part of `this specification," but I do" not limit 4 myself -to the embodimentcf the in- -25 vention herein described, as variousfcrms may be .adptved Scope of the claims.

-oscillographcffmy invention, V sl'iowi'ng diagram-I 'I 3p matically a preferred 'beanideflecting means,- A Figure 2 isa sectionalview of the electron fand concentration device utilized in the tube `o i Figurel.

It is well known -in theart that a cathode ray oscillograph tube, essentially comprises a means for.. producing electrons such as a thermionic cathode, and a luminescent screen against which electrons from thecathode may be projected in such a manner as to produce a small luminescent spot upon impact. Deflection means, either magnetic or electrostatic, may then be used to move the spot over adeilned area of the screen within the time limit of vision, so that either a trace or a picture field may be described. All of these prior art devices, however, have a common fault, namely, that electrons, being negative in charge, .tend to repel eachother within the beam, and,

as a consequence, the beam in many cases dif-V verges during its passage from cathode to screento such an extent that the spot energized by irnpact on the screen becomes so large and diffused that a sharp, well defined trace cannot' be se cured. Furthermore, accelerating anodes tend to cause.y even greater dispersion. Certain expedients have heretofore been used to prevent such against screen 2.

dispersion. .For example, a trace of inert gas may be left in the tube and the beam focused by the action of the gas. In other casesl electrostatic electron lenses have beenused, butl have found thatit is possible to maintain a concentratedv beam by sealing within the tube a smallelectromagnetic coil in such a position thatwhenenergizedits magnetic field will extend in the direc- 4tion' .ofelec'tron travel in the beam or. inasmuch asall elements, are usually' lined up' alongV the axis of the tube, thecoil will'be coeaxial with the meansfor producing the beam', and the screen.l My invention may be fully understood by direct reference to the drawing. Here an envelope I oi' the usual flask shapeis provided at the large end with. a fluorescent screen 2 deposited on the inside of the glass Wall. This fluorescent screen may be of willemite or any other known fluorescent or luminescent material. Atthe small end ,f which .is prefert'oroidal shape -zso out 'throughthefwalljof'the glass tube 9,'and the combined coil, lglass, tube, land anode-assembly is supportedon risers TI Iiand I v, whichare attachedto bands I 2.and I3 respectively; clamped around stem 3. Leads tov bands I2 and I3fare broughtto the outside Vof the envelope as are leads from the grid 5 and cathode 4. Riser lconnects not only to oneend of coil Q but also to anode 1, and riser Il connects to the other end of coil 8.

In operation the cathode 4 is heated by cathode battery I4, thus causing an emission of electrons. Anode 1 is energized to a positive potential from anode battery I5, and a small portion I6 of this battery is utilized to pass current through coil 8 bybeing connected thereto'through riser Il. l

The anode tube l, being energized to a positive potential with respect to cathode 4,-draws electrons therefrom through it and projects them The current, however, 'flowing through coil 8 from battery I6, causes a strong magnetic field to be-form-ed extending co-axially with the path ofthe electrons through the anode, thus keeping the electrons in a parallel stream and concentrating them on the screen. The electrons, therefore, both entering andleaving anode 1 are under the influence of this magnetic field, and therefore the stream as it leaves anode 1 going toward the screen tube tends to become concentrated, and any dispersion caused by the anode field or by their own inherent charges is greatly reduced, and a small, well dened spot is thus obtained.

While I have shown my coil l enclosed in the glass tube, this, of course, is not always necessary. 10 If insulated wire is utilized for coll 8 it is desirable to seal it within a tube in order that the organic materials utilized for insulation may not contaminate the vacuum within the tube. If, however, it is desirable that coil 8 be not sealed with- 15 in the special tube, bare wire may be wound on an insulating form and spaced to prevent short circuited terms. Even in this case it may be desirable to utilize glass for the form. In any event, the main feature of my invention is that a maggg netic coil is placed between cathode and screen so that a defined spot may be obtained, and I do not wish to be limited to any particular location of coil 8 with respect to the electrodes except that coil 8 shall be positioned co-axial with the path of the electrons between cathode and screen in the undeiiected portion of the path. This, naturally, means that the cathode, anode. screen and coil, shall be in co-axial relationship.

If the osclllograph is to be used to define a trace which varies in light intensity, then it is desirable that the strength of the electron beam be varied. Control electrode B may be energized from an input line I1 so that the strength of the beam may be varied in any convenient manner. I have also shown the beam as being deflected in two directions by magnetic coils I8 and I9, energized respectively by oscillators 20 and 2|.

An oscillograph made as herein described will give a wide field of view and sharp definition. It

is, therefore, ideally adapted for use in a telean electromagnetic coil within said enclosure and also surrounding said anode.

2. Apparatus *in accordance with claim 1, wherein the inner wall of said gas-tight enclosure is closely adjacent said anode and forms the chief positioning structure thereof.

. PHILO T. FARNSWORTH.- 

